This invention concerns stable aqueous dispersions of polyurethane-urea modified polyacrylics. Polyether or polyester urethane-urea emulsions are high Mw, thermoplastic type polymer dispersions which give outstanding mechanical properties in various applications. The balance of properties is believed to come from the block structure with rigid urea-urethane semi-crystalline phase in a flexible polyether or polyester matrix. Problems with these disperisons are poor rheology and thermoplastic behavior.
Polyether urethane polymers have less than optimum durability, especially in outdoor exposure, and polyester urethanes lack good hydrolysis resistance.
Polyurethanes based on aliphatic or cycloaliphatic di- or polyisocyanates are also high priced while those based on aromatic diisocyanates completely lack good outdoor durability due to yellowing on exposure. The typical thermoplastic behavior and poorer rheology is inherent to the technology of making high Mw polyurethane-urea dispersions since the many techniques (see a review article by Dieterich in Progress in Organic Coatings 9(1981 281-340) available for making such aqueous dispersions do not permit easy handling and control of functionality (acid, hydroxyl, amide, etc.) within the polymer architecture needed to give it thermoset behavior and built-in rheology. Acrylic dispersions or emulsions on the other hand prepared via free radical initiated reactions do easily allow the formulator to build in reactive groups to give the polymer the necessary rheological and thermoset behavior. It would therefore be preferable to combine the good rheological and thermoset properties of reactive acrylics with the outstanding mechanical properties of polyurethanes.
Both types of polymers, however, are in many cases incompatible due to large solubility parameter differences. Incompatibility does show up in many examples as a phase separation or complete kick-out of the mixed blend polyurethane-urea with acrylic or as a loss in film integrity and physical properties, when applied afterwards. The present invention provides for a method of making a polyurethane-urea modified polyacrylics in which the acrylic has functional groups such as hydroxyl, acid, amine and amide by chain extension of an acrylic dispersion or emulsion having primary or secondary amine groups to form a polyurethane-urea polyacrylic dispersion.